U.S. patent number 6,664,418 [Application Number 09/361,183] was granted by the patent office on 2003-12-16 for method for inhibiting polymerization of a vinyl compound.
This patent grant is currently assigned to Nippon Shokubai Co., Ltd.. Invention is credited to Sei Nakahara, Kazuo Ohkouchi, Kazuhiko Sakamoto, Masahiro Uemura, Masatoshi Ueoka.
United States Patent |
6,664,418 |
Sakamoto , et al. |
December 16, 2003 |
Method for inhibiting polymerization of a vinyl compound
Abstract
A method for inhibiting polymerization during transportation,
storage and/or production of (meth)acrylic acid or an ester thereof
includes adding an N-oxyl compound and water to a vinyl compound;
or dissolving an N-oxyl compound in water and adding the solution
to a vinyl compound in a process of recovering, purifying, and/or
synthesizing of the vinyl compound. The method can effectively
inhibit polymerization of the vinyl compound.
Inventors: |
Sakamoto; Kazuhiko (Hyogo-Ken,
JP), Ohkouchi; Kazuo (Hyogo-Ken, JP),
Uemura; Masahiro (Hyogo-Ken, JP), Nakahara; Sei
(Hyogo-Ken, JP), Ueoka; Masatoshi (Hyogo-Ken,
JP) |
Assignee: |
Nippon Shokubai Co., Ltd.
(Osaka, JP)
|
Family
ID: |
26518095 |
Appl.
No.: |
09/361,183 |
Filed: |
July 27, 1999 |
Foreign Application Priority Data
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Jul 27, 1998 [JP] |
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10-210505 |
Jul 27, 1998 [JP] |
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10-210506 |
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Current U.S.
Class: |
562/598; 560/205;
562/600 |
Current CPC
Class: |
C07B
63/04 (20130101); C07C 51/50 (20130101); C07C
51/50 (20130101); C07C 57/04 (20130101) |
Current International
Class: |
C07B
63/00 (20060101); C07B 63/04 (20060101); C07C
51/50 (20060101); C07C 51/42 (20060101); C07C
057/18 (); C07C 069/52 (); C07C 051/42 () |
Field of
Search: |
;560/205
;562/598,600 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1052847 |
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Jul 1991 |
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CN |
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0 620 206 |
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Oct 1994 |
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EP |
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0 620 206 |
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Oct 1994 |
|
EP |
|
0 685 447 |
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Dec 1995 |
|
EP |
|
0 685 447 |
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Dec 1995 |
|
EP |
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1127127 |
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Sep 1968 |
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GB |
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1 346 775 |
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Feb 1974 |
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GB |
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56-38301 |
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Apr 1981 |
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JP |
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60-36501 |
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Feb 1985 |
|
JP |
|
Other References
Zhao Ciyi, et al., "The Synthesis of .beta.-hydroxy Ethyl
Methacrylate and Distillation Polymerization Inhibitor Thereof,"
Journal of WUHAN Chemical Industry College, vol. 17, No. 4, pp.
20-23 w/English Abstract. .
Z. Li, et al., Chemistry of Synthetic High Polymers, CA 129:316591,
1 page, "Inhibiting Effect on the Radical Polymerization of Vinyl
Monomers," 1997 (Abstract Only)..
|
Primary Examiner: Rotman; Alan L.
Assistant Examiner: Oh; Taylor V.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A method for inhibiting polymerization of a vinyl compound
selected from the group consisting of (meth)acrylic acid and esters
of (meth)acrylic acid, during its storage and/or its transportation
comprising permitting a water soluble N-oxyl compound and 0.01-2
parts by weight of water to coexist in 100 parts by weight of the
vinyl compound, wherein the N-oxyl compound is at least one
selected from the group consisting of N-oxyl compounds represented
by the following general formula: ##STR2## wherein R.sup.1
represents CHOH, CHCH.sub.2 OH, CHCH.sub.2 CH.sub.2 OH, CHCOOH or
C.dbd.O, R.sup.2 represents H or CH.sub.2 OH.
2. A method according to claim 1, wherein the water soluble N-oxyl
compound and the water are added to the vinyl compound.
3. A method according to claim 1, wherein the water is added to a
mixture of the water soluble N-oxyl compound and the vinyl
compound.
4. A method according to claim 1, wherein the water soluble N-oxyl
compound is added to a mixture of the water and the vinyl
compound.
5. A method according to claim 1, wherein the vinyl compound is a
(meth)acrylic acid.
6. A method according to claim 1, wherein the water soluble N-oxyl
compound is added in 0.0005-0.1 parts by weight to 100 parts by
weight of the vinyl compound.
7. A method for inhibiting polymerization of a vinyl compound
selected from the group consisting of (meth)acrylic acid and esters
of (meth)acrylic acid, comprising the steps of: (i) dissolving an
N-oxyl compound in water, the amount of water being 1 to 1000 times
by weight that of the N-oxyl compound; the amount of water being
0.0005 to 10 parts by weight per 100 parts by weight of the vinyl
compound; and the amount of the N-oxyl compound being 0.0005 to 0.1
parts by weight per 100 parts by weight of the vinyl compound; and
(ii) adding the solution to the vinyl compound in a process of
recovering, purifying, and/or synthesizing of the vinyl
compound.
8. A method according to claim 7, wherein the vinyl compound is a
(meth)acrylic acid.
9. A method according to claim 7, wherein the N-oxyl compound is
one or more kinds selected from the groups consisting of N-oxyl
compounds represented by the following general formula;
##STR3##
wherein R.sup.1 represents CHOH, CHCH.sub.2 OH, CHCH.sub.2 CH.sub.2
OH, CHOCH.sub.2 OH, CHOCH.sub.2 CH.sub.2 OH, CHCOOH or C.dbd.O,
R.sup.2 represents H or CH.sub.2 OH.
10. A method according to claim 7, wherein the solution is added in
a collecting stage, a distilling stage and/or a purifying stage of
the process of recovering, purifying, and/or synthesizing of the
vinyl compound.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for inhibiting
polymerization of a vinyl compound. More particularly, the present
invention relates to a method for effectively inhibiting the
polymerization of (meth)acrylic acid or esters of (meth)acrylic
acid during these storage, transportation and production.
2. Description of the Prior Art
Vinyl compounds such as (meth)acrylic acid (i.e., acrylic acid or
methacrylic acid), esters of (meth)acrylic acid, and acrylonitrile
are prone to be naturally polymerized by light or heat due to the
vinyl bond they have. Therefore, there have been proposed to use
various polymerization inhibitors in order to inhibit
polymerization of (meth)acrylic acid or esters of (meth)acrylic
acid during their storage, transportation or production
process.
As an example, there has been proposed use of methoquinone.
Japanese Examined Patent Publication No. 414121 discloses a method
for inhibiting polymerization of vinyl compounds using an N-oxyl
compound such as bis-(2,2,6,6-tetramethyl-4-piperidino oxyl)
sebacate.
However, the inventors of the present application have studied the
stability of a vinyl compound during storage or transportation
after addition of the above-mentioned N-oxyl compound, and found
that the concentration of the N-oxyl compound gradually decreases
in contact with the vinyl compound, and it is difficult to prevent
polymerization of vinyl compounds for a prolonged time.
In the production process of vinyl compounds, particularly in the
processes of recovery, purification and synthesis of vinyl
compounds, polymerization of vinyl compounds proceeds. Therefore,
there have been proposed to use various polymerization inhibitors
in order to inhibit the polymerization of (meth)acrylic acid or
esters of (meth)acrylic acid during these processes.
For example, Japanese Examined Patent Publication No. 45-1054
discloses a method for inhibiting polymerization of acrylic acid
using an N-oxyl compound such as tertiary-butyl nitroxide and
4-hydroxy-2,2,6,6-tetramethyl-4-piperidino oxyl alone, gives better
polymerization inhibiting effect than that of the conventionally
known hydroquinone, pheno-thiazine, and cupric chloride etc.
Japanese Examined Patent Publication No. 54-3853 discloses a method
for inhibiting the polymerization using
4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl or
2,2,6,6-tetramethylpiperidino oxyl in the production process of
methacrylic acid from methacrolein using a gas containing oxygen in
an organic solvent.
Japanese Examined Patent Publication No. 58-46496 discloses a
method for inhibiting polymerization of (meth)acrylic acid or
esters of (meth)acrylic acid, using 3-oxo-2,2,5,5-tetramethyl
pyrolidino oxyl or 4-acetoxy 2,2,6,6-tetramethylpiperidino
oxyl.
Chinese Patent CN 1052847A discloses a method for inhibiting
polymerization of acrylic acid and esters of acrylic acid, using
4-hydroxy-2,2,6,6-tetramethylpiperldino oxyl alone or used in
combination with hydroquinone, which is shown to be higher than the
effect of combined use of copper dibutyldithiocarboxylate and
hydroquinone.
Japanese Unexamined Patent Publication No. 6-345681 discloses a
method for inhibiting polymerization of acrylic acid and esters of
acrylic acid, using N-oxyl compounds such as
2,2,6,6-tetramethylpiperldino oxyl, and
4,4',4"-tris(2,2,6,6-tetramethylpiperldino oxyl) phosphate in
combination with phenol compounds such as hydroquinone, and
phenothiazine compound.
Japanese Unexamined Patent Publication No. 9-316026 discloses a
method for inhibiting polymerization of acrylic acid and esters of
acrylic acid during its production, particularly during
distillation process, using an N-oxyl compound in combination with
phosphorus compound.
In the use of N-oxyl compounds according to the conventional
polymerization inhibiting technology in the production process, for
example, to prevent polymerization during distillation of crude
acrylic acid, an N-oxyl compound is dissolved in acrylic acid and
the solution is transferred to a distilling column by a pump.
The inventors found that the transfer of the solution, in which the
N-oxyl compound is dissolved in acrylic acid, to the distilling
tower in the recovery, purification and synthesis process of vinyl
compound as mentioned above does not sufficiently inhibit the
polymerization of vinyl compound.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for
inhibiting polymerization of a vinyl compound which has overcome
the problems residing in the prior art.
It is another object of the present invention to provide a method
for stabilizing and inhibiting polymerization of vinyl compounds
such as (meth)acrylic acid and ester of (meth)acrylic acid which
can reliably assure stabilization and inhibition of polymerization
of such vinyl compounds during storage, transportation and
production of them, in the presence of an N-oxyl compound and a
specific amount of water.
According to an aspect of the present invention, a method for
inhibiting polymerization of a vinyl compound uses an N-oxyl
compound and a specific amount of water. The presence of the N-oxyl
compound can inhibit polymerization of the vinyl compound more
effectively.
According to another aspect of the present invention, an N-oxyl
compound is dissolved in water to produce a solution, and the
solution is added to a vinyl compound in a process of recovering,
purifying, or synthesizing the vinyl compound. In this way,
polymerization of the vinyl compound can be effectively
inhibited.
The vinyl compound has a vinyl bond which is liable to cause
polymerization. Also, the N-oxyl compound includes any water
soluble N-oxyl compounds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to inhibition of polymerization
of (meth)acrylic acid and esters of (meth)acrylic acid.
Acrylic esters include methyl acrylate, ethyl acrylate, butyl
acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate,
2-hydroxypropyl acrylate and the like. Also, methacrylic esters
include methyl methacrylate, propyl methacrylate, 2-hydroxyethyl
methacrylate, 2-hydroxypropyl methacrylate and the like.
According to the present invention, any water soluble N-oxyl
compounds is useable. It is preferable to use
2,2,6,6-tetramethylpiperidino oxyls represented by the following
general formula (1); ##STR1##
wherein R.sup.1 represents CHOH, CHCH.sub.2 OH, CHCH.sub.2 CH.sub.2
OH, CHOCH.sub.2 OH, CHOCH.sub.2 CH, OH, CHCOOH or C.dbd.O, R.sup.2
represents H or CH.sub.2 OH.
The above-mentioned 2,2,6,6-tetramethylpiperidino oxyls include
4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl,
4-oxo-2,2,6,6-tetramethylpiperidino oxyl,
4-carboxy-2,2,6,6-tetramethylpiperidino oxyl, and the like. Among
these, preferably used are 4-hydroxy-2,2,6,6-tetramethylpiperidino
oxyl, 4-oxo-2,2,6,6-tetramethylpiperidino oxyl, and the like, and
particularly preferably used is
4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl. These N-oxyl
compounds may be used singly or at least two of these compounds may
be used in combination. In this case, the mixing ratio may be
appropriately decided.
More specifically, an N-oxyl compound may be preferably added in an
amount of 0.0005 parts by weight or more, more preferably 0.001
parts by weight or more, to 100 parts by weight of a vinyl compound
in order to ensure sufficient stabilization effects. On the other
hand, addition of an N-oxyl compound too much causes staining in a
produced acrylic acid. Accordingly, the amount may be preferably to
set an upper limit up to 0.1 parts by weight, more preferably up to
0.03 parts by weight.
The adding amount of water may be adjusted in accordance with the
solubility of water in the vinyl compound. It may be, however,
preferable to dissolve 0.01 parts by weight or more of water to 100
parts by weight of the vinyl compound, more preferably 0.02 parts
by weight or more, more preferably 0.05 parts by weight or more. To
assure the inhibiting effect, on the other hand, it may be
preferable to set the upper limit amount of water at 20 parts by
weight, preferably 5 parts by weight, more preferably 2 parts by
weight. If the adding amount of water is less than 0.01 parts by
weight, it is difficult to regulate the concentration of the N-oxyl
compound to a specified value, resulting in decomposition of the
N-oxyl compound and consequently insufficient inhibition effect.
While too much water will lower the stabilization effect thereof,
as water promotes the polymerization of the vinyl compound,
therefore the amount of water added shall be up to 20 parts by
weight.
The addition of N-oxyl compound and water to a vinyl compound is
not limited to a fixed sequence, but may be changed desirably.
However, it may be preferable -that an N-oxyl compound is firstly
dissolved in water and then the resulting N-oxyl compound aqueous
solution is added to a vinyl compound. Also, it may be possible to
add an N-oxyl compound into a mixture of a vinyl compound and
water. In this way, there coexist three components, i.e., N-oxyl
compound, vinyl compound and water. It could be presumed that this
coexistence of the three components exerts the polymerization
inhibiting effect.
The present invention may be applicable to vinyl compounds which
contain impurities as by-product in the production process, or
impurities contained in the starting raw materials of a vinyl
compound. For acrylic acid containing various impurities, e.g.,
organic acids such as acetic acid, aldehydes such as acrolein, for
example, the inhibiting effect can be attainable.
Further, it may be possible to use conventional polymerization
inhibitors such as phenothiazine, methoquinone, copper
dialkyldithiocarbamate, manganese acetate, and p-phenylenediamine,
in addition to the inventive polymerization inhibitor.
Owing to the coexistence of an N-oxyl compound and a specific
amount of water in a vinyl compound, the decrease in the
concentration of the N-oxyl compound can be suppressed for a
prolonged time. The coexistence of an N-oxyl compound and a
specific amount of water in a vinyl compound delays the time for
initiating polymerization more than the conventional inhibitors,
thus inhibiting polymerization of a vinyl compound in the storage
or transportation more effectively.
Further, a method for inhibiting -the polymerization, according to
the present inventive method, during production of a vinyl compound
will be explained in detail.
A vinyl compound in a process of recovery, purification and
synthesis is kept from polymerizing by dissolving an N-oxyl
compound in water, and adding the solution into the vinyl
compound.
Conventionally, acrylic acid is produced from a reaction gas
obtained by two stage catalytic oxidation reaction of propylene by
the processes of: (1) collecting an acrylic acid in the form of an
aqueous solution by making a reaction mixture gas containing
acrylic acid in contact with water; (2) distilling the acrylic acid
aqueous solution in the presence of an azo-tropic solvent and
recovering crude acrylic acid; and (3) purifying the crude acrylic
acid. The purifying process (3) includes distillation of separating
substances having low boiling points such as acetic acid,
distillation of separating substances having low boiling points
such as unreacted acrolein, and distillation of separating
substances having high boiling points.
The present invention is applicable for inhibition of
polymerization of acrylic acid in any of the above-mentioned
processes i.e., (1) collecting process, (2) recovering process, and
(3) purifying process.
The addition of an aqueous solution of an N-oxyl compound is not
limited to a particular manner, but may be carried out in a desired
manner. For example, the aqueous solution of N-oxyl compound may be
directly introduced into a vinyl compound in each process. In the
case of purifying processor also, it may be introduced into in a
supply line or a refluxing line.
An aqueous solution of an N-oxyl compound may be added only in the
collecting process (1), or in each of the processes of collecting
process (1), recovering process (2) and purifying process (3)
(including various distillations). It may be preferable to add the
aqueous solution in each process or each distillation stage.
In the case of adding -the aqueous solution in each process, it may
be preferable to set the lower limit of adding amount of N-oxyl
compound at 0.0005 parts by weight, more preferably 0.001 parts by
weight, more preferably 0.002 parts by weight to 100 parts by
weight of a vinyl compound in each process. The upper limit may be
preferable to set at 0.1 parts by weight, more preferably 0.03
parts by weight, more preferably 0.02 parts by weight to 100 parts
by weight of vinyl compound in each process.
If the adding amount of N-oxyl compound is less than 0.0005 parts
by weight, the necessary polymerization inhibiting effect cannot be
attained. In particular, if the operation temperature is more than
100.degree. C., the inhibiting effect noticeably lowers. On the
other hand, if an N-oxyl compound is added more than 0.1 parts by
weight, the product of acrylic acid is liable to be stained.
The amount of water in which an N-oxyl compound is dissolved may be
changed in accordance with the kind and the amount of an N-oxyl
compound used as well as the kind of process. However, it may be
preferable to set the lower limit at 0.0005 parts by weight, more
preferably 0.001 parts by weight, more preferably 0.002 parts by
weight to 100 parts by weight of a vinyl compound in each process.
If the amount of water is more than 10 parts by weight, on the
other hand, the purity of the product of acrylic acid undesirably
lowers. Accordingly, the upper limit for water may be set at 10
parts by weight, preferably 1 part by weight, more preferably 0.2
part by weight.
The concentration of an N-oxyl compound in an N-oxyl compound
aqueous solution may be regulated in accordance with the kind of
N-oxyl compound or the allowable amount of water. However, it may
be preferable to set the upper limit at around 80 percent of the
saturation solubility of the N-oxyl compound in water at a normal
temperature to prevent precipitation of the N-oxyl compound in a
tank storing the N-oxyl compound aqueous solution. On the other
hand, the lower limit of the concentration of a N-oxyl compound
depends on the amount of the N-oxyl compound to be added or the
characteristic performance of an adding apparatus. However, it may
be preferable to set the lower limit at around 0.1 weight
percent.
The effect of inhibiting polymerization of a vinyl compound in the
production process according to the present invention is not
obtained simply because water coexists with the N-oxyl compound in
each process or in each distillation stage. According to the
present invention, regardless of the presence of water in the
production process, the use of water as a solvent for N-oxyl
compound, which means the N-oxyl compound is dissolved in water
first and the aqueous solution is then added to the above-described
process, is significant condition to exert the effect of inhibiting
polymerization of a vinyl compound in the production process.
For example, in the collecting process (1), water is introduced to
collect an acrylic acid. In the recovering process (2), the acrylic
acid aqueous solution is introduced and distilled. Accordingly,
water exists in each process location or tower. However, in the
collecting process (1), the case in which an N-oxyl compound is
added in the form of an aqueous solution inhibits polymerization of
acrylic acid more effectively than the case in which the N-oxyl
compound is added in the form of an acrylic acid solution (see
Example 5 and Comparative Example 2). Accordingly, it could be seen
that the addition of an N-oxyl compound in the form of an aqueous
solution, which is in accordance with a method of the present
invention, enhances the polymerization inhibiting effect of N-oxyl
compound.
As mentioned above, in the collecting process (1) and the
recovering process (2), there exists water. However, water is
separated in each process. Accordingly, even if water exists in
relatively large amount in these processes, there is no problem. On
the contrary, in the distillation stage of -the purifying process
(3), the amount of water should be kept in the specified range to
prevent the purity of the product from lowering.
For example, in the collecting process (1) and the recovering
process (2), the amount of water may be 1-1000 times by weight that
of an N-oxyl compound, and in the purifying process (3), the amount
of water may be 1-200 times by weight that of an N-oxyl compound in
a distillation stage for separating substances having a low boiling
point, and it is 1-50 times by weight in a distillation stage for
separating substances having a high boiling point.
According to the present invention, molecular oxygen may be used
concurrently, thereby enhancing the inhibition of polymerization of
a vinyl compounds. As means of supplying molecular oxygen, it may
be possible to adopt bubbling, or alternatively dissolve molecular
oxygen in a solvent, and add the solution in a vinyl compound. For
example, in the purifying process (3), molecular oxygen may be
supplied from the bottom of a stripper tower or reboller in the
form of gas. It may be preferable to supply molecular oxygen in an
amount of 0.1 percent by volume or more with respect to the amount
of evaporated vinyl compound. This is because of the fact that if
it is less than 0.1 percent by volume, remarkable effect cannot be
attainable. The upper limit of molecular oxygen to be supplied may
be determined based the operation performance of distilling
equipment. However, a large amount of supply requires
reconstruction of the equipment. Accordingly, it may be preferable
to supply molecular oxygen in not more than 1.0 percent by
volume.
In addition to acrylic acid, the present invention may be
applicable to other vinyl compounds.
The term "production", "recovering", "purifying", and
"synthesizing" means the reaction process of a vinyl compound, and
the above-mentioned processes (1)-(3). Further, such terms include
a modification of the abovementioned process and any additional
distilling process for separating a substance having a specified
boiling point and the like.
In the case of acrylic acid, these terms respectively correspond to
an oxidation process of propylene, recovering, purifying and
synthesizing processes of acrylic acid. In the case of methacrylic
acid, these terms respectively correspond to processes of
separating, collecting, refining methacrylic acid from a reaction
gas containing methacrylic acid obtained by catalytic gas phase
oxidation of isobutylene. In the case of (meth)acrylic ester, these
terms respectively correspond to processes of esterifying and
purifying in addition to the above-mentioned processes of
(meth)acrylic acid.
The present invention will be further described with reference to
the following Examples. All the ppm is based on weight.
EXAMPLE 1
A solution in which water in an amount of 2-0 parts by weight to
100 parts by weight of acrylic acid to be treated, and
4-hydroxy-2,2,6,6-tetramethylpiperldino oxyl (hereinafter
abbreviated as 4H-TEMPO) in an amount of 0.03 parts by weight to
100 parts by weight of the acrylic acid were dissolved in acrylic
acid was stored at the room temperature in a sample bottle and the
concentration of 4H TEMPO in the acrylic acid was measured 30
minutes, 2 hours and 10 hours after the dissolution. The results
were as follows. No decrease in the concentration of 4H-TEMPO was
observed even after 10 hours. Initial amount: 300 ppm After 30
minutes: 300 ppm After 2 hours: 300 ppm After 10 hours: 300 ppm
EXAMPLE 2
The concentration of 4H-TEM-PO in acrylic acid was measured in a
process similar to that of Example 1, except that the amount of
water added was 0.03 parts by weight to 100 parts by weight of the
acrylic acid. The results are as follows: About 60% of the initial
concentration of 4H-TEMPO still remained after 2 hours and about
34% of the initial concentration of 4H-TEMPO still remained after
10 hours. Initial amount: 300 ppm After 30 minutes: 204 ppm After 2
hours: 174 ppm After 10 hours: 103 ppm
EXAMPLE 3
The concentration of 4H-TEMPO in acrylic acid was measured in a
process similar to that of Example 1, except that the amount of
water added was 0.1 parts by weight to 100 parts by weight of the
acrylic acid. The results are as follows: About 80% of the initial
concentration of 4H-TEMPO still remained after 2 hours and About
60% of the initial concentration of 4H-TEMPO still remained after
10 hours. Initial amount: 300 ppm After 30 minutes: 275 ppm After 2
hours: 243 ppm After 10 hours: 180 ppm
COMPARATIVE EXAMPLE 1
The concentration of 4H-TEMPO in acrylic acid was measured in a
process similar to that of Example 1, except that-the amount of
water added was 0.005 parts by weight to 100 parts of the acrylic
acid. The results are as follows: The concentration of 4H-TEMPO
reduced to one third of the initial concentration after 2 hours and
about 3% of the initial concentration of 4H-TEMPO remained after 10
hours. Initial amount: 300 ppm After 30 minutes: 152 ppm After 2
hours: 98 ppm After 10 hours: 10 ppm
From the comparison of the Examples 1-3 with the Comparative
Example 1, it is clear that when a specific amount of water is
added together with 4H-TEMPO, the reduction in the concentration of
4H-TEMPO with time can be controlled and the acrylic acid can be
stably maintained.
EXAMPLE 4
5 ml of a solution comprising acrylic acid, water in such an amount
that is given in Table 1 and 4H-TEMPO in an amount of 0.0001 parts
by weight to 100 parts by weight of acrylic acid was added to a
test tube and immersed in an oil bath which was kept at 80.degree.
C. and the time required until the viscosity starts to increase was
measured as the -time for initiating polymerization. The results
are given in Table 1.
TABLE 1 Time for initiating Amount of water added polymerization
Sample No. (parts by weight) (hour) 1 2 50 2 5 36 3 10 30 4 15 27 5
25 19 6 43 15 7 67 8 8 100 7 9 150 4
Note: The amount of water added is based on weight to 100 parts by
weight of the acrylic acid
As seen from Table 1, in Samples in which the amount of water added
is up to 20 parts by weight to 100 parts by weight of acrylic acid,
i.e., Sample Nos. 1-4, the time for initiating polymerization was
25 hours or more, however, when more than 20 parts by weight of
water were added (No. 5-No. 9), the time for initiating
polymerization was less than 20 hours. In Samples in which water of
up to 5 parts by weight were added, .+-..e., Sample Nos. 1 and 2,
the time for initiating polymerization was at least 35 hours or
more, showing that the range is more preferable for inhibiting the
polymerization of acrylic acid more effectively at an elevated
temperature.
By employing the polymerization inhibiting method of the present
invention, the induction time can be extended longer than before,
and polymerization can be more effectively inhibited.
EXAMPLE 5
The effect of inhibiting polymerization in the collecting process
(1) was confirmed.
Propylene was subjected to gas phase oxidation using a gas
containing molecular oxygen in the presence of an oxidizing
catalyst to give a reaction mixture gas comprising 0.68 kg/hr of
acrylic acid, 0.02 kg/hr of acetic acid and 0.45 kg/hr of water.
The reaction mixture gas was introduced to a gas collecting tower
in which a cascade mini ring (inner diameter of 14 mm) was packed
by a height of 6000 mm, a gas blow-off tube was provided at the top
of the tower, a reaction mixture gas supply pipe at the lower part
of the tower, and a tower bottom liquid extract pipe at the bottom
of the tower, and the collection operation of the reaction mixture
gas was carried out using water as an absorbing liquid.
During the collection process,
4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl aqueous solution was
used as a polymerization inhibitor and an aqueous solution thereof
was introduced at 0.02 kg/hr from the top of the tower. The amount
of the polymerization inhibitor used was 0.003 parts by weight to
100 parts by weight of the acrylic acid and the amount of water
used was 2.9 parts by weight to 100 parts by weight of the acrylic
acid.
The operation was carried out at the tower top temperature of
63.degree. C., tower bottom temperature of 67.degree. C. and
acrylic acid aqueous solution of 0-6 kg/hr was obtained through the
bottom of the tower in the stationary state. The polymerization
inhibition effect was confirmed by the viscosity of the liquid
taken out through the bottom of the tower and the examination of
the overhauled tower.
The operation was carried out continuously under the
above-mentioned conditions for about 20 days and always stable
condition was obtained and no generation of a polymer was found at
all when the collecting tower was examined after the operation was
stopped.
COMPARATIVE EXAMPLE 2
The collection operation was carried out in the same way as that
used in Example 4 except that
4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl was used as a
polymerization inhibitor which was dissolved in acrylic acid and
added.
7 days after the start of the operation the viscosity of the liquid
taken out through the bottom of the tower was observed to increase.
The operation was stopped and the tower was overhauled and the
generation of the polymer was observed in the tower.
EXAMPLE 6
The polymerization inhibiting effect in the recovering process (2)
was confirmed. Acrylic acid aqueous solution was distilled using a
packed tower having an outlet pipe, a refluxing liquid supply pipe
and a polymerization inhibitor solution supply pipe at the top of
the tower, a raw material supply pipe at the middle of the tower,
and a kettle, a tower bottom liquid extract pipe and an oxygen
supply pipe at the bottom of the tower. The acrylic acid aqueous
solution was an acrylic acid aqueous solution containing 30% by
weight of water which was obtained by contacting water with a
reaction mixture gas obtained by catalytic gas phase oxidation of
propylene. The acrylic acid aqueous solution was supplied to the
above-mentioned packed tower at 100 ml/hr. Distillation was carried
out using toluene as a refluxing liquid, under such conditions that
tower top pressure of 190 mmHg, tower top temperature of 50.degree.
C., and tower bottom temperature of 100.degree. C.
A polymerization inhibitor of a given amount was added to and
dissolved in a solvent as shown in Table 2, then the obtained
polymerization inhibiting solution was added from the top of the
tower into the packed tower and oxygen gas of 0-3% by volume based
on the amount of the evaporated acrylic acid vapor was supplied to
the bottom of the tower. The amount of the polymerization inhibitor
added was based on the amount of the acrylic acid supplied to the
packed tower. The composition of the liquid taken out from the
bottom of the tower in the steady state comprised 97% by weight of
acrylic acid, 0.02% by weight of water and 2.98% by weight of
others. As the refluxing liquid, the distilled oil phase was
recycled and used. After operating for 8 hours, inside of the tower
was dried by aspirating with a vacuum pump having minimum pressure
of 5.times.10.sup.-4 Torr from the lower part of the tower for 15
hours at a room temperature, and the weight of the polymer
generated in the tower was measured to evaluate the polymerization
inhibiting effect. The results are given in Table 2.
TABLE 2 Polymerization Solvent Amount of inhibitor (Note 1) used
for dissolving the produced Sample Amount polymerization inhibitor
polymer No. Kind (ppm) (Note 2) (g) 1 4H-TEMPO 100 Water 0.9 2 Same
as above 50 Water 1.7 3 Same as above 100 Refluxing liquid 3.8
(toluene) 4 Same as above 100 Acrylic Acid 5.8 5 4-Oxo-TEMPO 100
Water 0.8 6 Same as above 100 Refluxing liquid 4.0 (toluene) 7 Same
as above 100 Acrylic acid 1 (Note 1) The amount of polymerization
inhibiting agent was based on weight to 100 parts by weight of
acrylic acid. (Note 2) Each solvent was supplied in an amount of
0.82 parts by weight to 100 parts by weight of acrylic acid in the
raw material.
The abbreviations used in Table 2 represent the following
compounds. The same abbreviations are made in Tables 3, 4, and 5.
4H-TEMPO: 4-hydroxy-2,2,6,6-tetramethylpiperldino oxyl 4-Oxo-TEMPO:
4-oxo-2,2,6,6-tetramethylpiperldino oxyl.
As it is clear from Table 2, 4H-TEMPO dissolved in water and added
(Sample Nos-1, 2 and 5) inhibits the polymerization of acrylic acid
effectively as a smaller amount of a polymer is generated compared
to the case in which the agent is dissolved in toluene or acrylic
acid and added.
EXAMPLE 7
Distillation of an acrylic acid aqueous solution was carried out in
the process similar to that used in Example 6 except that methyl
isobutyl ketone was used as the refluxing liquid. The results are
given in Table 3.
TABLE 3 Polymerization Solvent Amount of inhibitor (Note 1) used
for dissolving the produced Sample Amount polymerization inhibitor
polymer No. Kind (ppm) (Note 2) (g) 1 4H-TEMPO 100 Water 1.2 2 Same
as above 50 Water 2.6 3 Same as above 100 Refluxing liquid 5.4
(methyl isobutyl ketone) 4 Same as above 100 Acrylic Acid 8.9 5
4-Oxo-TEMPO 100 Water 1.3 6 Same as above 100 Refluxing liquid 6.7
(methyl isobutyl ketone) 7 Same as above 100 Acrylic acid 9.5 (Note
1) The amount of polymerization inhibiting agent was based on
weight to 100 parts by weight of acrylic acid. (Note 2) Each
solvent was supplied in an amount of 0.82 parts by weight to 100
parts by weight of acrylic acid in the raw material.
As it is clear from Table 3, 4H-TEMPO dissolved in water and added
(sample Nos. 1, 2 and 5) inhibits the polymerization of acrylic
acid effectively as a smaller amount of a polymer is generated
compared to the case in which the agent is dissolved in methyl
isobutyl ketone or acrylic acid and added.
EXAMPLE 8
Distillation of an acrylic acid aqueous solution was carried out in
the process similar to that used in Example 6 except that a mixed
solvent of methyl isobutyl ketone and toluene (mixed at 65:35 by
weight) was used as the refluxing liquid. The results are given in
Table 4
TABLE 4 Polymerization Solvent Amount of inhibitor (Note 1) used
for dissolving the produced Sample Amount polymerization inhibitor
polymer No. Kind (ppm) (Note 2) (g) 1 4H-TEMPO 100 Water 0.3 2 Same
as above 50 Water 0.9 3 Same as above 100 Refluxing liquid 2.4
(methyl isobutyl 4 Same as above 100 ketone + toluene) 3.7 5
4-Oxo-TEMPO 100 Acrylic Acid 0.3 6 Same as above 100 Water 2.9
Refluxing liquid 7 Same as above 100 (methyl isobutyl 4.1 ketone +
toluene) Acrylic acid (Note 1) The amount of polymerization
inhibiting agent was based on weight to 100 parts by weight of
acrylic acid. (Note 2) Each solvent was supplied in an amount of
0-82 parts by weight -to 100 parts by weight of acrylic acid in the
raw material.
As it is clear from Table 4, 4H-TEMPO dissolved in water and added
(No. 1, No. 2 and No. 5) inhibits the polymerization of acrylic
acid effectively as a smaller amount of a polymer is generated
compared to the case in which the agent is dissolved in the mixed
solvent of methyl isobutyl ketone and toluene or acrylic acid and
added.
EXAMPLE 9
Distillation of an acrylic acid aqueous solution was carried out in
the process similar to that used in Example 6 except that a mixed
solvent of methyl methacrylate and toluene (mixed at 35:65 by
weight) was used as the refluxing liquid. The result is given in
Table 5.
TABLE 5 Polymerization Solvent Amount of inhibitor (Note 1) used
for dissolving the produced Sample Amount polymerization inhibitor
polymer No. Kind (ppm) (Note 2) (g) 1 4H-TEMPO 100 Water 0.2 2 Same
as above 50 Water 0.7 3 Same as above 100 Refluxing liquid 2.1
(methyl methacrylate + 4 Same as above 100 toluene) 3.5 5
4-Oxo-TEMPO 100 Acrylic Acid 0.3 6 Same as above 100 Water 2.8
Refluxing liquid 7 Same as above 100 (methyl methacrylate + 4.5
toluene) Acrylic acid (Note 1) The amount of polymerization
inhibiting agent was based on weight to 100 parts by weight of
acrylic acid. (Note 2) Each solvent was supplied in an amount of
0.82 parts by weight to 100 parts by weight of acrylic acid in the
raw material.
As it is clear from Table 5, 4H-TEMPO dissolved in water and added
(No. 1, No. 2 and No. 5) inhibits the polymerization of acrylic
acid effectively as a smaller amount of a polymer is generated
compared to the case in which the agent is dissolved in the mixed
solvent of methyl methacrylate and toluene or acrylic acid and
added.
The present invention can be carried out in various other forms
without departing from the spirit and main features thereof.
Therefore, the above-mentioned Examples are considered as
illustrative only in every aspect and cannot be understood to limit
the present invention. The scope of the present invention is shown
by the claims and the text of the specification does not restrict
it in any way. All the modifications and equivalents may be
regarded as falling within the scope of the invention in the
appended claims and -their equivalents.
EXAMPLE 10
5 ml of a solution comprising acrylic acid water in such an amount
that is given in Table 6 and 4H-TEMPO in an amount of 0.001 parts
by weight to 100 parts by weight of acrylic acid was added to a
test tube and immersed in an oil bath which was kept at 80.degree.
C. and the time required until the viscosity starts to increase was
measured as the time for initiating polymerization. The results are
given in Table 6.
TABLE 6 Amount of water added Time for initiating Sample No. (Parts
by weight) polymerization (hour) 1 1.5 614 2 4 435 3 15 307 4 30
148 5 100 65
Note: The amount of water added is based on weight to 100 parts by
weight of the acrylic acid.
As seen in Table 6, in Samples in which the amount of water added
is up to 20 parts by weight to 100 parts by weight of acrylic acid,
i.e., Sample Nos 1-2, the time for initiating polymerization was
300 hours or more, however, when more than 20 parts by weight of
water were added (No.4 and No. 5), the time for initiating
polymerization was less than 150 hours. In Samples in which water
of up to 5 parts by weight were added, i.e., Sample Nos. 1 and 2,
the time for initiating polymerization was at least 400 hours or
more, showing that the range is more preferable for inhibiting the
polymerization of acrylic acid more effectively at an elevated
temperature.
By employing the polymerization inhibiting method of the present
invention, the induction time can be extended longer than before,
and polmerization can be more effectively inhibited.
The priority documents of the present application, Japanese Patent
Application Nos. 10-210505 and 10-210506 filed Jul. 27, 1998, are
hereby incorporated by reference.
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